The Isle of Wight Council has announced the official options for the future management of Undercliff Drive in preparation for discussion at a public meeting on Monday.
The council has been handed six options from Ramboll to rectify the land movement damage from February, which left nine properties inaccessible by vehicle.
The first option involves simply re-establishing pedestrian access using self-drill anchors and a pedestrian barrier, which will reduce requirements for stabilisation but increase the need for regular monitoring, inspection and repair and does not address the long term geological risks.
The most expensive option involves repairing and reopening the through road from Ventnor to Niton using reinforced soil block with hard facing, drainage and strand anchors, and building a pile-supported road deck. This will provide long term stabilisation and is resistant to an increased range of geological failures but Ramboll raised many issues that would occur during construction, such as lack of access and environmental concerns.
The council could also choose to repair and re-open road with access from only one direction using self-drill anchors and deep wells, and reinforced soil block and drainage. This is the faster method, more in keeping with the previous work that addresses the overall geological failure mechanism but raises many of the same construction issues as the most expensive option, such as the discharge of water, which may require new outfall to sea.
The remaining three options are: establishing a new access road to properties along the base of the cliff requiring slope stabilisation using bolting and netting as well as rock fall protection, or a temporary low cost road from the west, or permanent closure to vehicles of the affected part of Undercliff Drive and pedestrian access limited to residents.
Estimated costs run from £100,000 to £20M and councillor Jon Gilby, executive member for resources and highways PFI, has made it clear that without more details on construction costs it was not possible to determine which of the potential schemes would be preferred.
Gilbey added: “It is appropriate that officers investigate which of the possible options suggested by Island Roads can be delivered at an affordable cost, whilst considering the wider threats to Undercliff Drive from on-going instability problems.”
Subsidence at the two main locations has slowed, but not stopped, and further ground movement has been identified at several locations away from the two major failure areas.
The report by the PFI roads organisation Island Roads last month concluded that the current ground anchor solution is no longer suitable but works would have to be delayed until ground movement stops.
Island Roads is continuing to monitor groundwater levels as well as surface and sub-surface groundwater movement at the location.